The number of personnel is fewer than the roughly 780 monitors and observers who were dispatched in 2012. The Justice Department has said its poll-watching presence has been curtailed by a 2013 Supreme Court opinion that gutted a key provision of the Voting Rights Acts. That has led to a reduction in trained observers, who enjoy unfettered access to the polls and cannot be removed from the sites.

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Most of the more than 500 staffers will be monitors, who rely on the cooperation of local officials to do their jobs. Observers in this election are limited to a handful of jurisdictions around the country where federal court orders are in place that authorize their presence.

Justice Department officials say they hope voters will not detect any difference in the federal presence.

Among the states receiving federal monitors are those that have changed their voting rights laws since the last presidential election, including North Carolina, or that have reported problems in past elections.

"In most cases, voters on the ground will see very little practical difference between monitors and observers," Vanita Gupta, head of the department's Civil Rights Division, said in a statement. "We work closely and cooperatively with jurisdictions around the country to ensure that trained personnel are able to keep an eye on the proceedings from an immediate vantage point."